Isolated Flying Capacitor Multilevel Converters

Abstract

This paper presents the topology known as the isolated flying capacitor multilevel flyback converter (FCMFC). The topology uses isolated flying capacitors (FC) for high-gain, DC-DC power conversion while maintaining primary-secondary isolation and improving the efficiency and capability of a standard flyback transformer circuit. Three converters have been developed and tested, one flyback as a control, a 3 level FCMFC, and a 4 level FCMFC to prove the gain and efficiency benefits of this new topology. The FCMFC prototypes achieve higher gain and efficiencies relative to a flyback design utilizing the same off-theshelf transformer. The stress of the input and output switches is reduced because of the fractioning of the output voltage across multiple output stages, allowing future iterations to utilize lowerrated components. The operating parameters are 5V to 40V boosting for a 10W load at 250kHz. Utilizing the same semiconductor components, the flyback converter control prototype achieves 78% efficiency while the proposed FCMFC converters reach 85% and 82% efficiency, even with the added isolated power, gate drive, and bootstrap circuitry. The FCMFCs have a multiplying effect on the gain of the traditional flyback which also increases near the 90% duty cycle flyback threshold. Additional testing was done at light load and at 100kHz, 250kHz, 452kHz, and 500kHz.

Medium-Voltage Seven-Level Multiplexed Converter for AC Applications

“…Multilevel based power converter architectures have also been investigated for DC-DC applications as in [11], [12]. It is imperative to choose the proper conversion topology and technology to enhance the characteristics of the multilevel converters, such as efficiency, power density, and quality of the input currents and output voltages.…”